This invention relates to a regulated alternator having a positive fault related shut down apparatus to prevent damage to the alternator and/or the connected loads.
Separate alternator power supply systems are used in industry for providing of appropriate electrical power to various loads. A voltage regulator is connected in the control circuit of the alternator to establish and maintain a predetermined voltage output under varying load and operating conditions. The regulator often includes various current limit devices to minimize the current output under certain operating and voltage conditions and thereby prevent damage to the alternator and/or the interconnected loads.
In a typical system a rotating field alternator is energized with a rectified current from an exciter generator. The excitation of the exciter generator is controlled by the voltage regulator to in turn control the output of the alternator in accordance with various voltage, current and other related sensed operating parameters. The power supply for the exciter and the voltage regulator may be provided with a feedback power from the main alternator or may advantageously be powered from a separate permanent magnet generator constructed as an integrated part of the alternator assembly. For example a particularly satisfactory permanent magnet generator alternator system is shown in the co-pending application of M. Parshall entitled "Permanent Magnet Generator Apparatus" and filed on even date herewith. The system with a separate power supply insures a constant voltage supply and continued operation of the voltage regulator independently of the proper operation of the alternator.
Under certain conditions the voltage regulation system may malfunction with the alternator continuing to operate in an adverse or damaging state. Generally, an external circuit or the output of the alternator is fused to open the output circuit and positively prevent and effectively shut down the alternator under such conditions. In such systems however, the protective device may not always function for various reasons including a faulty or oversized fuse in place, or even a deliberate bypass of the fuse structure by the operating personnel which will prevent appropriate response. Further, other conditions might exist under which the regulator should have shut down the alternator but because of some internal malfunction in the regulator system, the alternator is driven to continue to provide an output, in essence, without regulation.
Thus, in a regulated alternator, regulator failure and/or a power device failure to a short circuit condition, will generally cause the regulator to create a full forcing excitation of the alternator excitation system. The maximum voltage and current is then supplied to the excitation system unless a suitable protective switching device such as a fuse, circuit breaker, or like device is activated to positively open the excitation power supply and positively shut down the alternator. The protective devices are necessarily carefully constructed and rated to permit limited full forcing excitation while establishing a tripped or open state when necessary to protect the system. The problem is made more difficult because of severe environments in which alternator power systems often operate, such as, salt, fog, vibration, various air born foreign matter and the like. Further, the protective device should be conveniently available for effective resetting if the shut down was due to a self correcting problem or after other correction of the problem. The availability however will permit the operator to by-pass the protective device in order to establish a voltage supply in spite of the failure in the regulator.
There is therefore a need for a separate monitoring system to insure shut down of the alternator under such conditions to protect the alternator as well as the loads connected to the alternator.